Extrasolar Planets extrasolar = outside of (external to) our solar system.
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Transcript of Extrasolar Planets extrasolar = outside of (external to) our solar system.
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Extrasolar Planets
extrasolar = outside of (external to) our solar system
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How can we discover planets?
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How can we discover planets?
1. Try to image them
2. Observe the motion of the star as it gets pulled by theplanet
3. Look at stars and wait for planets to go in front of them,making the stars temporarily dimmer
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1. Imaging
Techniques for finding extrasolar planets
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Here are some extrasolar planets
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These are all fake. Why is it hard to image planets?
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Can you think of a way around the problem?
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Can you think of a way around the problem?
SOHO spacecraftimage of the sunwith a coronagraph
?
Telescope image ofSaturn, rings and moons with a coronagraph
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What kinds of planets would be easiest to image?
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What could you learn abouta planet if you had an
image of it?
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Fomalhaut
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HR 8799
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Beta Pictorisa
Combination of two near-infrared images obtained with the Very Large Telescope
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It is difficult to directly image planets. Only a few
planets have been detected with this method.
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2. Stellar “Wobble”
Techniques for finding extrasolar planets
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Is the sun influenced by the gravitational force of the
planets?
Does Jupiter orbit around the center of the sun?
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Stars and planets orbit aroundtheir center of mass
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Stars and planets orbit aroundtheir center of mass
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Suppose Jupiter and the Sun could be placed on a see-saw. Which point is closest to the center of balance?
A B C D
Size of sun, Jupiter roughly to scale.
Sizes and distances not to scale with each other.
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Note that the star is much brighter than the planet, so we observe the motion of the star produced by the planet. This is called an “indirect detection technique”.
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Now, how do we observe this wobble?
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How do we observe stellar wobble?
First, let’s talk about the Doppler Shift. Think about whathappens to the sound when an ambulance passes by.
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How do we observe stellar wobble?
The same thing happens to light.
Looks “red”
Looks “blue”
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How do we observe stellar wobble?
(animationradialvelocitydemo.html)
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How do we observe stellar wobble?
(Here’s what the data actually look like)
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What kind of planets would be easiest to observe with the
stellar wobbletechnique?
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What could you learn abouta planet if you found it with
thestellar wobble technique?
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We don’t know the inclination of the planet’s orbit
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Which of these two orientations would produce the largest
Doppler shift?
A B
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We don’t know the inclination of the planet’s orbit
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The Doppler technique only provides the minimum mass of the planet if the orientation is not known (which is most of the time).
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The first planets were detected with this method, and to date, hundreds of
planets have been detected with this method.
Before 2009, nearly all planets were detected with
this method.
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3. Planetary “Transit”
Techniques for finding extrasolar planets
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Planetary Transit
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Transit of sun by Venus
http://apod.nasa.gov/apod/ap120611.html
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Transit of sun by Venus
Telescopic H-alpha image from Chris Hetlage
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Transit of sun by Venus
Image of Venus transit from Taj Mahal by Kevin Frayer
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Transit of sun by Mercury
Images of Mercury transit from SOHO satellite
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Transits are easier to detect if the planet is
(A) large (B) small
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What would you learn about a planet if you found it with
the planetary transit technique?
(A) Its radius(B) Its mass(C) Its orbital period(D) Both its radius and its orbital period
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A special geometry is needed for a transit Transits are rare
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Transits get
(A) more (B) less
likely as the planet’s orbit gets larger.
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The Kepler Mission
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The Kepler mission has now discovered thousands
of planets!
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The three extrasolar planet detection techniques are:
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The three extrasolar planet detection techniques are:
1. Direct imaging
2. The “wobble” or “Doppler shift” technique
3. The transit method
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What are extrasolar planets like?
Are they similar to the planets in the solar
system?
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http://www.astronomy.ohio-state.edu/~microfun/ob06109/
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